Short answers, pulled from the story.
HIV is a retrovirus that attacks the immune system, primarily infecting CD4 positive T cells, macrophages and dendritic cells. Without treatment it can progress to acquired immunodeficiency syndrome, or AIDS, defined by a CD4 count below 0.2 cells per millilitre or specific associated diseases. It destroys CD4 cells, leaving the body open to opportunistic infections and cancers.
AIDS was first clinically reported on the 5th of June 1981, with five cases in the United States, and the CDC began referring to the disease as AIDS by September 1982. In 1983, the research groups of Robert Gallo and Luc Montagnier published findings on a novel retrovirus, and in 1986 their isolates, HTLV-III and LAV, were renamed HIV.
HIV spreads by three main routes: sexual contact, exposure to infected blood or tissues, and from mother to child during pregnancy, delivery or breastfeeding. Blood transfusion with infected blood transmits the virus in about 90 percent of cases, while saliva, sweat, tears and urine do not transmit it unless contaminated with blood. Mosquitoes cannot transmit HIV.
There is no cure or vaccine for HIV, but highly active antiretroviral therapy slows the disease and makes it a manageable chronic condition. Treatment cuts the death rate by 80 percent and raises life expectancy for a newly diagnosed young adult to 20 to 50 years. A person with an undetectable viral load on long-term treatment has effectively no risk of transmitting HIV sexually.
Both HIV-1 and HIV-2 originated in non-human primates in west-central Africa and crossed to humans in the early 20th century. HIV-1 arose in southern Cameroon from SIVcpz, a simian immunodeficiency virus of chimpanzees, while HIV-2's closest relative is SIVsmm of the sooty mangabey. Genetic studies date the most recent common ancestor of the HIV-1 M group to around 1910.
Between the first recognition of AIDS and 2024, the disease is estimated to have caused at least 42.3 million deaths worldwide. In 2023, about 630,000 people died from HIV-related causes, an estimated 1.3 million people acquired HIV, and roughly 39.9 million people were living with HIV, 65 percent of them in the WHO African Region.